Damping valve

ABSTRACT

A damping valve includes a valve seat member provided with a port, a valve body that opens or closes the port, a tubular spool that abuts on a side of the valve body opposite to the valve seat member, a spool holding member that has an outer circumference where the spool is mounted movably along an axial direction, a ring mounted to the outer circumference of the spool holding member, the ring contacting slidably with an inner circumference of the spool, and a back-pressure chamber partitioned by the spool and the spool holding member, the back-pressure chamber being configured to bias the spool such that the valve body is pressed toward the valve seat member using an internal pressure, wherein the internal pressure of the back-pressure chamber is applied to an inner circumferential side of the ring.

TECHNICAL FIELD

This invention relates to a damping valve.

BACKGROUND ART

There is known a type of damping valve, called a variable damping valve,capable of changing a damping force of a shock absorber interposedbetween a chassis and an axle of a vehicle. Such a type of damping valveincludes, for example, an annular valve seat provided in the middle of aflow path connected from a cylinder of the shock absorber to areservoir, a valve body seated on or unseated from the annular valveseat to open or close the flow path, a pilot passage branching from theflow path, an orifice provided in the middle of the pilot passage, atubular spool abutting on a side of the valve body opposite to the valveseat, a valve housing having an outer circumference where the spool isslidably mounted and forming a back-pressure chamber in a rear side ofthe valve body along with the spool, a pilot valve provided downstreamof the pilot passage, and a solenoid for adjusting a valve openingpressure of the pilot valve. In the variable damping valve, a secondarypressure downstream from the orifice in the pilot passage is introducedinto the back-pressure chamber to press the valve body.

In the damping valve described above, since the pilot valve is provideddownstream from the back-pressure chamber, the secondary pressure guidedto the back-pressure chamber is controlled by the valve opening pressureof the pilot valve by adjusting the valve opening pressure of the pilotvalve using a thrust force of the solenoid.

As described above, the secondary pressure is applied to the rear faceof the valve body, so that the valve body is pressed to the valve seatside. A pressure upstream of the flow path is applied to the front faceof the valve body by flexing the valve body to unseat it from the valveseat. Therefore, if the force of unseating the valve body from the valveseat caused by the pressure upstream of the flow path exceeds the forceof pressing the valve body to the valve seat caused by the secondarypressure, the valve body is opened.

That is, it is possible to adjust the valve opening pressure of thevalve body by controlling the secondary pressure. In addition, it ispossible to change resistance applied from the damping valve to a flowof the hydraulic oil passing through the flow path by adjusting thevalve opening pressure of the pilot valve using the solenoid. Therefore,it is possible to generate a desired damping force in the shock absorber(for example, see JP 2009-222136 A).

SUMMARY OF INVENTION

In the damping valve described above, the back-pressure chamber isformed as the spool makes sliding contact with the outer circumferenceof the valve housing. Although the damping force can be changed byadjusting the internal pressure of the back-pressure chamber, a controlrange thereof is not wide.

In addition, if a clearance (gap) between the spool and the valvehousing is not managed appropriately, a leakage amount of the hydraulicoil between the spool and the valve housing varies. As a result, thedamping force generated by the damping valve also variesdisadvantageously.

In view of the aforementioned problems, it is therefore an object ofthis invention to provide a damping valve capable of widening a controlrange of the damping force while exerting a stable damping force.

According to one aspect of the present invention, a damping valveincludes a valve seat member provided with a port, a valve body thatopens or closes the port, a tubular spool that abuts on a side of thevalve body opposite to the valve seat member, a spool holding memberthat has an outer circumference where the spool is mounted movably alongan axial direction, a ring mounted to the outer circumference of thespool holding member, the ring contacting slidably with an innercircumference of the spool, and a back-pressure chamber partitioned bythe spool and the spool holding member, the back-pressure chamber beingconfigured to bias the spool such that the valve body is pressed towardthe valve seat member using an internal pressure, wherein the internalpressure of the back-pressure chamber is applied to an innercircumferential side of the ring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a damping valve accordingto an embodiment of this invention.

FIG. 2 is a cross-sectional view illustrating a shock absorber providedwith the damping valve according to an embodiment of this invention.

FIG. 3 is a diagram illustrating a damping characteristic of the shockabsorber provided with the damping valve according to an embodiment ofthis invention.

FIG. 4 is a diagram illustrating a damping characteristic of a shockabsorber provided with a damping valve according to a modification.

FIG. 5 is an enlarged cross-sectional view illustrating a pilot valve ofthe damping valve according to an embodiment of this invention.

FIG. 6 is a diagram illustrating a temporal change of a displacementamount of a valve body after the pilot valve is opened.

FIG. 7 is a partially enlarged cross-sectional view illustrating adamping valve according to another embodiment of this invention.

FIG. 8 is a partially enlarged cross-sectional view illustrating adamping valve according to still another embodiment of this invention.

DESCRIPTION OF EMBODIMENTS

A description will now be made for embodiments of this invention withreference to the accompanying drawings.

Referring to FIG. 1, a damping valve V includes a valve seat member 1having a port 1 a, a valve body 3 for opening or closing the port 1 a, atubular spool 30 abutting on a side of the valve body 3 opposite to thevalve seat member 1, a valve housing 20 serving as a spool holdingmember and having an outer circumference where the spool 30 is mountedmovably along an axial direction, a back-pressure chamber P partitionedby the spool 30 and the valve housing 20 that biases the spool 30 suchthat the valve body 3 is pressed toward the valve seat member 1 with aninternal pressure, and a ring 29 mounted to the outer circumference ofthe valve housing 20 to make sliding contact with an inner circumferenceof the spool 30.

The damping valve V is installed in a shock absorber S. The shockabsorber S is generally designed to generate a damping force by applyingresistance to a fluid passing through the port 1 a in the course ofexpansion or contraction.

Referring to FIG. 2, the shock absorber S installed with the dampingvalve V includes, for example, a cylinder 10, a piston 11 slidablyinserted into the cylinder 10, a rod 12 retractably inserted into thecylinder 10 and connected to the piston 11, a rod-side chamber 13 and apiston-side chamber 14 partitioned by the piston 11 inserted into thecylinder 10, an intermediate tube 16 that covers an outer circumferenceof the cylinder 10 to form a discharge passage 15 along with thecylinder 10, and an outer tube 18 that covers an outer circumference ofthe intermediate tube 16 to form a reservoir 17 along with theintermediate tube 16. Hydraulic oil as a hydraulic fluid is filled inthe rod-side chamber 13, the piston-side chamber 14, and the reservoir17. The reservoir 17 is also filled with gas in addition to thehydraulic oil. As the hydraulic fluid, any fluid capable of exerting adamping force may be employed instead of the hydraulic oil.

The shock absorber S includes an inlet channel 19 that allows only for aflow of the hydraulic oil directed from the reservoir 17 to thepiston-side chamber 14, and a piston passage 56 provided in the piston12 to allow only for a flow of the hydraulic oil directed from thepiston-side chamber 14 to the rod-side chamber 13. The discharge passage15 causes the rod-side chamber 13 and the reservoir 17 to communicatewith each other, and the damping valve V is provided in the middle ofthe discharge passage 15.

When the shock absorber S is operated to contract, the piston 11 movesdownward in FIG. 2, so that the piston-side chamber 14 is compressed,and the hydraulic oil inside the piston-side chamber 14 moves to therod-side chamber 13 through the piston passage 56. In this case, sincethe rod 12 intrudes into the cylinder 10, the hydraulic oil becomesexcessive inside the cylinder 10 as much as a volume of the intrudingrod, and the excessive hydraulic oil is extruded from the cylinder 10and is discharged to the reservoir 17 through the discharge passage 15.The shock absorber S exerts a contractive damping force by applyingresistance to a flow of the hydraulic oil moving to the reservoir 17through the discharge passage 15 using the damping valve V to increasean internal pressure of the cylinder 10.

When the shock absorber S is operated to expand, the piston 11 movesupward in FIG. 2, so that the rod-side chamber 13 is compressed, and thehydraulic oil inside the rod-side chamber 13 moves to the reservoir 17through the discharge passage 15. In this case, the piston 11 movesupward, and the volume of the piston-side chamber 14 increases, so thatthe hydraulic oil corresponding to this increasing volume is suppliedfrom the reservoir 17 through the inlet channel 19. The shock absorber Sexerts an expansive damping force by applying resistance to a flow ofthe hydraulic oil moving to the reservoir 17 through the dischargepassage 15 using the damping valve V to increase an internal pressure ofthe rod-side chamber 13.

As described above, the shock absorber S is a uni-flow type shockabsorber in which the hydraulic oil is discharged from the cylinder 10to the reservoir 17 through the discharge passage 15, and the hydraulicoil circulates in a uni-directional manner in the order of thepiston-side chamber 14, the rod-side chamber 13, and the reservoir 17 ineither the expanding or contracting operation. That is, the shockabsorber S is designed to generate both the expansive and contractivedamping forces using a single damping valve V.

In the shock absorber S, the amount of hydraulic oil discharged from thecylinder 10 can be set to be the same between the expanding andcontracting operations if the cross-sectional area of the rod 12 is setto a half of the cross-sectional area of the piston 11, and the piston11 moves by the same amplitude. Therefore, by setting the resistanceapplied by the damping valve V to the flow to be the same, it ispossible to set the expansive and contractive damping forces to be thesame.

The damping valve V according to this embodiment includes a valve seatmember 1 fitted to a sleeve 16 a provided in an opening of theintermediate tube 16, a subsidiary valve body 2 floatably mounted to anouter circumference of an assembly shaft 1 c provided in the valve seatmember 1 and seated on or unseated from the first valve seat 1 b, avalve body 3 similarly mounted to the outer circumference of theassembly shaft 1 c provided in the valve seat member 1, a valve-bodyintermediate chamber C provided between the subsidiary valve body 2 andthe valve body 3, and a restrictive passage 2 b that causes the port 1 aand the valve-body intermediate chamber C to communicate with eachother.

The damping valve V further includes a cavity valve housing 20 connectedto the assembly shaft 1 c of the valve seat member 1, a tubular pilotvalve seat member 21 housed in the valve housing 20, a pilot valve body22 slidably inserted into the pilot valve seat member 21, and a solenoidSol exerting a thrust force to the pilot valve body 22. A pilot passage23 for reducing the pressure upstream of the port 1 a and guiding it tothe back-pressure chamber P is provided in the valve seat member 1 andthe inside of the valve housing 20.

As illustrated in FIG. 1, the valve seat member 1 includes alarge-diameter basal portion 1 d fitted to the sleeve 16 a, an assemblyshaft 1 c protruding from the basal portion 1 d toward the pilot valveseat member 21, a cavity 1 e formed to penetrate through the basalportion 1 d and the assembly shaft 1 c in an axial direction to form apart of the pilot passage 23, an orifice 1 f provided in the middle ofthe cavity 1 e, a plurality of ports 1 a penetrating through the basalportion 1 d, and an annular first valve seat 1 b formed in an end of thebasal portion 1 d in the pilot valve seat member 21 side and in an outercircumferential side of the exit of the port 1 a.

The port 1 a penetrates through the basal portion 1 d of the valve seatmember 1 as described above. An opening of the port 1 a in the innercircumferential side of the basal portion 1 d communicates with therod-side chamber 13 via the discharge passage 15 formed in theintermediate tube 16, and an opening of the port 1 a in the subsidiaryvalve body 2 side communicates with the reservoir 17. That is, the shockabsorber S is designed to discharge the hydraulic oil from the rod-sidechamber 13 to the reservoir 17 through the discharge passage 15 and theport 1 a during expansion or contraction operation, and the upstream ofthe port 1 a serves as the rod-side chamber 13. In addition, similar tothe port 1 a, the cavity 1 e communicates with the rod-side chamber 13via the discharge passage 15.

In the valve seat member 1, a small diameter portion 1 g obtained byreducing a diameter of the basal portion 1 d in the discharge passage 15side is fitted to the sleeve 16 a, and a seal ring 24 is mounted to anouter circumference of the small diameter portion 1 g. As a result, agap between the small diameter portion 1 g and the sleeve 16 a is sealedso as to prevent the discharge passage 15 from communicating with thereservoir 17 through the outer circumference of the basal portion 1 d.

The subsidiary valve body 2 seated on or unseated from the first valveseat 1 b to open or close the port 1 a is stacked on an end of the basalportion 1 d of the valve seat member 1 opposite to the small diameterportion 1 g. The subsidiary valve body 2 having an annular shapeincludes an annular second valve seat 2 a protruding oppositely to thevalve seat member 1, and a restrictive passage 2 b that is opened fromthe inner circumferential side of the second valve seat 2 a andcommunicates with the surface of the valve seat member 1 side.

The end of the exit of the port 1 a is blocked by the subsidiary valvebody 2 while the subsidiary valve body 2 is seated on the first valveseat 1 b. The restrictive passage 2 b is configured to apply resistanceto a flow of the passing hydraulic oil. Although described below in moredetail, as the hydraulic oil passing through the port 1 a passes throughthe restrictive passage 2 b and moves to the rear side of the subsidiaryvalve body 2, that is, oppositely to the valve seat member 1, adifferential pressure is generated between the front side of thesubsidiary valve body 2, that is, the valve seat member 1 side, and therear side.

The subsidiary valve body 2 is slidably mounted to an outercircumference of an annular spacer 25 mounted to the outer circumferenceof the assembly shaft 1 c of the valve seat member 1. A thickness of thespacer 25 in the axial direction is larger than a thickness of the innercircumference of the subsidiary valve body 2 in the axial direction, andthe subsidiary valve body 2 is configured such that the outercircumference of the spacer 25 can move in the axial direction. As aresult, the subsidiary valve body 2 is assembled with the valve seatmember 1 floatably. The subsidiary valve body 2 is seated on or unseatedfrom the first valve seat 1 b by approaching or receding from the valveseat member 1, and the port 1 a is opened as the subsidiary valve body 2is unseated from the first valve seat 1 b.

The valve body 3 is stacked on the rear side of the subsidiary valvebody 2. The valve body 3 is an annular laminated leaf valve. The innercircumference of the valve body 3 is assembled with the assembly shaft 1c, and is interposed between the spacer 25 and the valve housing 20screwed to the assembly shaft 1 c. Therefore, the valve body 3 can beflexed toward the outer circumferential side so as to be seated on orunseated from the second valve seat 2 a of the subsidiary valve body 2.

The inner circumference of the valve body 3 is stacked on the spacer 25,and the outer circumference of the valve body 3 is seated on the secondvalve seat 2 a. Therefore, a valve-body intermediate chamber C is formedbetween the valve body 3 and the subsidiary valve body 2. The valve-bodyintermediate chamber C communicates with the port 1 a via therestrictive passage 2 b. As the valve body 3 is flexed and is unseatedfrom the second valve seat 2 a by a pressure applied to the valve-bodyintermediate chamber C via the restrictive passage 2 b, an annular gapis formed between the subsidiary valve body 2 and the valve body 3. As aresult, the hydraulic oil passing through the port 1 a and therestrictive passage 2 b can move to the reservoir 17 through the gapbetween the valve body 3 and the subsidiary valve body 2. That is, evenwhen the subsidiary valve body 2 is seated on the first valve seat 1 b,the port 1 a is opened, and communication to the reservoir 17 isobtained if the valve body 3 is flexed and is unseated from the secondvalve seat 2 a. That is, the valve body 3 is configured to open or closethe port 1 a.

As the valve body 3 is flexed, and the subsidiary valve body 2 is raisedby a pressure received from the port 1 a, the subsidiary valve body 2slides on the outer circumference of the spacer 25 and is unseated fromthe first valve seat 1 a. In this case, the hydraulic oil passingthrough the port 1 a is discharged to the reservoir 17 through theannular gap formed between the subsidiary valve body 2 and the firstvalve seat 1 a.

The valve body 3 is a laminated leaf valve obtained by stacking aplurality of annular plates. The number of the annular plates is set toan arbitrary number. A cutout orifice 3 a is provided in the outercircumference of the annular plate of the valve body 3 seated on thesecond valve seat 2 a. The orifice may be provided by forming a notch orthe like in the second valve seat 2 a of the subsidiary valve body 2except for the valve body 3 or may be provided in the first valve seat 1b of the valve seat member 1 or a portion of the subsidiary valve body 2abutting on the first valve seat 1 b.

The restrictive passage 2 b may be formed in any configuration if it cancause the front and rear sides of the subsidiary valve body 2 tocommunicate with each other. For example, the restrictive passage 2 bmay be provided in any place other than the subsidiary valve body 2. Ifthe restrictive passage 2 b is provided in the subsidiary valve body 2,it is possible to facilitate fabrication.

A washer 26, an annular plate spring 27, and a washer 28 are stackedsequentially in the side of the valve body 3 opposite to the subsidiaryvalve body 2 and are assembled to the assembly shaft 1 c. The valvehousing 20 is screwed to the leading end of the assembly shaft 1 c. As aresult, the spacer 25, the valve body 3, the washer 26, the plate spring27, and the washer 28 assembled to the assembly shaft 1 c are fixedbetween the basal portion 1 d of the valve seat member 1 and the valvehousing 20.

The subsidiary valve body 2 mounted to the outer circumference of thespacer 25 is movable along the axial direction.

The inner circumferential side of the plate spring 27 is fixed to theassembly shaft 1 c, and the outer circumferential side thereof serves asa free end.

As illustrated in FIG. 1, the valve housing 20 includes a small-diametertubular portion 20 a having a tubular shape and a small outer diameter,a large-diameter tubular portion 20 b having a large outer diameter, anannular groove 20 c provided in the outer circumference of thelarge-diameter tubular portion 20 b, a pressure introduction horizontalhole 20 d opened in the annular groove 20 c to communicate with theinner circumference of the large-diameter tubular portion 20 b, and apressure introduction vertical hole 20 e opened in the end of thelarge-diameter tubular portion 20 b in the small-diameter tubularportion 20 a side to communicate with the pressure introductionhorizontal hole 20 d.

The valve housing 20 is connected to the valve seat member 1 by screwingthe screw hole portion 20 f provided inward of the small-diametertubular portion 20 a into the assembly shaft 1 c of the valve seatmember 1. The end of the large-diameter tubular portion 20 b opposite tothe small-diameter tubular portion 20 a is provided with an annularprotrusion 20 g in the inner circumferential side and a plurality oftooling holes 20 h opened in the edge. The valve housing 20 can beeasily screwed into the assembly shaft 1 c by inserting a tool to thetooling holes 20 h and rotating it.

A synthetic resin ring 29 is mounted to the annular groove 20 c of thevalve housing 20. A tubular spool 30 is slidably mounted to the outercircumference of the ring 29. That is, the spool 30 is movable along theaxial direction with respect to the valve housing 20.

A flange 30 a protruding inward is provided in an end of the spool 30 inthe valve body 3 side. The flange 30 a has an annular projection 30 bprotruding toward the valve body 3.

The outer circumference of the plate spring 27 abuts on the end of theflange 30 a opposite to the annular projection 30 b. The spool 30 isbiased by the plate spring 27 toward the valve body 3, and the annularprojection 30 b abuts on the surface of the valve body 3 opposite to thesubsidiary valve body 2.

The spool 30 partitions and forms the back-pressure chamber P incooperation with the valve housing 20 between the spool 30 and the valvehousing 20. The back-pressure chamber P communicates with the valvehousing 20 via the pressure introduction vertical hole 20 e and thepressure introduction horizontal hole 20 d as its end of the valve body3 side is blocked by the plate spring 27. The inside of the valvehousing 20 communicates with the cavity 1 e of the valve seat member 1and communicates with the rod-side chamber 13 upstream of the port 1 avia the orifice 1 f. The hydraulic oil discharged from the rod-sidechamber 13 is guided to the back-pressure chamber P through the orifice1 f, and the pressure upstream of the port 1 a is reduced by the orifice1 f and is introduced into the back-pressure chamber P.

The rear face of the valve body 3 receives a biasing force for pressingthe valve body 3 toward the subsidiary valve body 2 by virtue of aninternal pressure of the back-pressure chamber P in addition to thebiasing force of the plate spring 27 for biasing the spool 30. That is,when the shock absorber S is operated to expand or contract, thesubsidiary valve body 2 receives the internal pressure of the rod-sidechamber 13 from the front side through the port 1 a, and the internalpressure of the back-pressure chamber P and the biasing force caused bythe plate spring 27 from the rear side via the valve body 3.

A force obtained by multiplying the pressure of the back-pressurechamber P by a cross-sectional area of the inner diameter of the spool30 in the valve housing 20 side rather than the flange 30 a is exertedto the valve body 3 to approach the subsidiary valve body 2. Inaddition, a force obtained by multiplying the pressure of the valve-bodyintermediate chamber C by a cross-sectional area of the inner diameterof the second valve seat 2 a is exerted to the valve body 3 to recedefrom the subsidiary valve body 2. A ratio between the cross-sectionalarea of the inner diameter of the spool 30 in the valve housing 20 siderather than the flange 30 a and the cross-sectional area of the innerdiameter of the second valve seat 2 a defines a pressure boosting ratioas a ratio of the valve opening pressure of the valve body 3 against theinternal pressure of the back-pressure chamber P. It is noted that ahole may be provided in the plate spring 27 to directly apply theinternal pressure of the back-pressure chamber P to the valve body 3.

As the internal pressure of the valve-body intermediate chamber Cincreases by the internal pressure of the rod-side chamber 13, a forceof flexing the outer circumference of the valve body 3 toward the spool30 surpasses the internal pressure of the back-pressure chamber P andthe biasing force caused by the plate spring 27, the valve body 3 isflexed and is unseated from the second valve seat 2 a to form a gapbetween the valve body 3 and the subsidiary valve body 2, so that theport 1 a is opened.

According to this embodiment, the inner diameter of the second valveseat 2 a is larger than the inner diameter of the first valve seat 1 b,and an area of the subsidiary valve body 2 pressed from the port 1 aside is different from an area of the subsidiary valve body 2 pressedfrom the valve-body intermediate chamber C side. Therefore, if thedifferential pressure generated by the restrictive passage 2 b does notreach the valve opening pressure for unseating the subsidiary valve body2 from the first valve seat 1 b, the subsidiary valve body 2 remains tobe seated on the first valve seat 1 b.

Meanwhile, as the differential pressure generated by the restrictivepassage 2 b reaches the valve opening pressure for unseating thesubsidiary valve body 2 from the first valve seat 1 b while the valvebody 3 is flexed to have an opened state, the subsidiary valve body 2 isalso unseated from the first valve seat 1 b to open the port 1 a. Thatis, according to this embodiment, the pressure boosting ratio of thevalve body 3 is set to be smaller than the pressure boosting ratio ofthe subsidiary valve body 2 which is a ratio of the valve openingpressure of the subsidiary valve body 2 against the pressure of thevalve-body intermediate chamber C, and the internal pressure of therod-side chamber 13 for the opening operation of the valve body 3 islower than the internal pressure of the rod-side chamber 13 for theopening operation of the subsidiary valve body 2. That is, the valveopening pressure of the valve body 3 is set to be lower than that of thesubsidiary valve body 2.

The annular groove 20 c installed with the ring 29 communicates with thepressure introduction horizontal hole 20 d. As a result, the ring 29 ispressed toward the spool 30 by the pressure received from the pressureintroduction horizontal hole 20 d. Therefore, as the pressure upstreamof the port 1 a increases, a force of pressing the ring 29 increases.

The ring 29 may be formed of, for example, a material resistant toabrasion of the sliding surface of the spool 30, such as fluororesin,synthetic resin, or brass. In addition, in order to facilitateinstallation of the ring 29 to the annular groove 20 c, a bias cut(partition) 29 a may be applied to the ring 29. When the ring 29 isprovided with the bias cut 29 a, it is possible to easily enlarge thediameter of the ring 29 using the pressure of the inner circumferentialside, and easily suppress movement of the spool 30.

The tubular pilot valve seat member 21 is housed in the inside of thevalve housing 20 in the side where the annular protrusion 20 g ratherthan the screw hole portion 20 f is provided.

The pilot valve seat member 21 includes a bottomed cylindrical valvecontainer 21 a, a flange portion 21 b provided protrudingly outward inthe outer circumference of the opening-side end of the valve container21 a, a penetrating hole 21 c opened from the lateral side of the valvecontainer 21 a to communicate with the inside, an annular pilot valveseat 21 d provided in the opening-side end of the valve container 21 aprotrudingly in the axial direction, and an annular valve catch 21 eprovided in the outer circumference of the flange portion 21 b to bethicker than the flange portion 21 b.

A failsafe valve body 31 having an annular laminated leaf valve ismounted to the outer circumference of the annular protrusion 20 g of thevalve housing 20. The failsafe valve body 31 is interposed between asurface of the large-diameter tubular portion 20 b of the valve housing20 where the annular protrusion 20 g is provided and the valve catch 21e of the pilot valve seat member 21. As a result, the innercircumference of the failsafe valve body 31 is fixed, and the outercircumference of the failsafe valve body 31 can be flexed.

The pilot valve body 22 is slidably inserted into the valve container 21a of the pilot valve seat member 21. The pilot valve body 22 includes asmall diameter portion 22 a provided in the pilot valve seat member 21side and slidably inserted into the valve container 21 a, a largediameter portion 22 b provided oppositely to the pilot valve seat member21, an annular concave portion 22 c provided between the small diameterportion 22 a and the large diameter portion 22 b, a flange-like springshoe 22 d provided in the outer circumference of the end opposite to thepilot valve seat member 21, a communicating channel 22 e penetratingfrom one end of the pilot valve body 22 to the other end, an orifice 22f provided in the middle of the communicating channel 22 e, and anannular projection 22 g provided in the outer circumference of the endof the spring shoe 22 d opposite to the pilot valve seat member 21.

The concave portion 22 c of the pilot valve body 22 faces thepenetrating hole 21 c at all times when the pilot valve body 22 movesalong the axial direction with respect to the pilot valve seat member21. That is, the pilot valve body 22 does not block the penetrating hole21 c as long as the pilot valve body 22 is allowed to move.

As described above, with respect to the concave portion 22 c, an outerdiameter of the pilot valve body 22 in the side opposite to the pilotvalve seat member 21 is large, and the end of the large diameter portion22 b in the pilot valve seat member 21 side is provided with an annularsitting portion 22 h facing the pilot valve seat 21 d. As the pilotvalve body 22 moves along the axial direction with respect to the pilotvalve seat member 21, the sitting portion 22 h is seated on or unseatedfrom the pilot valve seat 21 d. That is, the pilot valve body 22 and thepilot valve seat member 21 constitute the pilot valve Pi, so that thepilot valve Pi is closed as the sitting portion 22 h sits on the pilotvalve seat 21 d.

A perforated disc 32 fitted to the inner circumference of the annularprojection 22 g is stacked on the end of the spring shoe 22 d oppositeto the pilot valve seat member 21. The communicating channel 22 ecommunicates with the rear side of the perforated disc 32 opposite tothe pilot valve body 22 through a hole (not shown) of the perforateddisc 32. A coil spring 33 that biases the pilot valve body 22 oppositelyto the pilot valve seat member 21 is interposed between the spring shoe22 d and the flange portion 21 b.

The pilot valve body 22 is biased by the coil spring 33 oppositely tothe pilot valve seat member 21 at all times. Therefore, if a thrustforce is not exerted from the solenoid Sol described below against thecoil spring 33, the pilot valve Pi is opened. According to thisembodiment, the pilot valve body 22 is biased to recede from the pilotvalve seat member 21 using the coil spring 33. However, any otherelastic material capable of exerting a biasing force may be employedinstead of the coil spring 33.

As the pilot valve body 22 is inserted into the valve container 21 a ofthe pilot valve seat member 21, a space K is formed closer to the bottomside of the valve container 21 a than the penetrating hole 21 c insidethe valve container 21 a. The space K communicates with the outside ofthe pilot valve Pi via the communicating channel 22 e and the orifice 22f provided in the pilot valve body 22. As a result, when the pilot valvebody 22 moves along the axial direction with respect to the pilot valveseat member 21, the space K serves as a dash pot, so that it is possibleto suppress abrupt displacement of the pilot valve body 22 and avibrating motion of the pilot valve body 22.

A failsafe valve seat member 34 stacked on the large-diameter tubularportion 20 b side of the valve housing 20 is provided in the outercircumference of the pilot valve body 22. The failsafe valve seat member34 includes an annular socket portion 34 a provided in the outercircumference and fitted to the outer circumference of thelarge-diameter tubular portion 20 b of the valve housing 20, an annularwindow 34 b provided in the end of the valve housing 20 side, a failsafevalve seat 34 c provided in the outer circumference of the annularwindow 34 b, an annular concave portion 34 d provided in the innercircumferential side of the annular window 34 b, a plurality of channels34 e formed from the inner circumference to the annular concave portion34 d to communicate with the annular window 34 b, an annular flange 34 fprovided in the inner circumference on the end opposite to the valvehousing 20 to protrude inward, a plurality of notches 34 g provided inthe end opposite to the valve housing 20, and a through-hole 34 hpenetrating through the socket portion 34 a.

The inner diameter of the failsafe valve seat member 34 excluding theflange 34 f is set not to hinder movement of the pilot valve body 22. Asthe pilot valve body 22 is biased by the coil spring 33 while no thrustforce is received from the solenoid Sol, the outer circumference of theannular projection 22 g of the pilot valve body 22 abuts on the flange34 f so as to prevent further movement oppositely to the valve housing20. As a result, it is possible to block an opening end of the failsafevalve seat member 34 opposite to the valve housing 20 using the pilotvalve body 22.

As the failsafe valve seat member 34 is stacked on the valve housing 20,the valve catch 21 e of the pilot valve seat member 21 is interposedbetween the failsafe valve seat member 34 and the valve housing 20 alongwith the failsafe valve body 31, so as to fix the pilot valve seatmember 21 and the failsafe valve body 31. The valve container 21 a ofthe pilot valve seat member 21 is housed in the valve housing 20. Inthis case, by fitting the outer circumference of the valve catch 21 e tothe annular concave portion 34 d provided in the failsafe valve seatmember 34, the pilot valve seat member 21 is positioned in the failsafevalve seat member 34 in the radial direction.

The failsafe valve body 31 is seated on the failsafe valve seat 34 cprovided in the failsafe valve seat member 34 to block the annularwindow 34 b. The failsafe valve body 31 is unseated from the failsafevalve seat 34 c to open the annular window 34 b as it is flexed byvirtue of the pressure from the annular window 34 b, so that the insideof the failsafe valve seat member 34 communicates with the reservoir 17via the channel 34 e and the through-hole 34 h. In this manner,according to this embodiment, the failsafe valve body 31 and thefailsafe valve seat member 34 constitute the failsafe valve F. Thechannel 34 e is formed by a trench provided in the valve housing 20 sideof the failsafe valve seat member 34. Therefore, it is possible tofacilitate fabrication. Naturally, instead of the trench, a hole may beformed as the channel 34 e.

As described above, the damping valve V causes the rod-side chamber 13and the reservoir 17 to communicate with each other using the port 1 a,and the port 1 a is opened or closed by the subsidiary valve body 2 andthe valve body 3. In addition to the route passing through the port 1 a,the pilot passage 23 for causing the rod-side chamber 13 and thereservoir 17 to communicate with each other is formed by the cavity 1 eof the valve seat member 1, the inside of the valve housing 20, thepenetrating hole 21 c of the pilot valve seat member 21, the inside ofthe pilot valve seat member 21, the concave portion 22 c of the pilotvalve body 22, the inside of the failsafe valve seat member 34, and thenotch 34 g of the failsafe valve seat member 34.

The pilot passage 23 communicates with the back-pressure chamber P viathe pressure introduction vertical hole 20 e and the pressureintroduction horizontal hole 20 d provided in the valve housing 20, sothat the pressure upstream of the port 1 a is reduced by the orifice 1 fprovided in the middle of the pilot passage 23 and is introduced intothe back-pressure chamber P. In addition, the pilot passage 23 is openedor closed by the pilot valve Pi, so that it is possible to control theinternal pressure of the back-pressure chamber P by controlling theopening level of the pilot valve Pi. The shock absorber S is providedwith the solenoid Sol for exerting a thrust force to the pilot valvebody 22 in order to control the opening level of the pilot valve Pi.

As the pilot valve body 22 is biased by the coil spring 33, and theouter circumference of the annular projection 22 g abuts on the flange34 f, the communication between the notch 34 g and the inside of thefailsafe valve seat member 34 is disconnected. If the internal pressureof the pilot passage 23 increases in this state and reaches the valveopening pressure of the failsafe valve body 31, the failsafe valve body31 is unseated from the failsafe valve seat 34 c. As a result, it ispossible to cause the pilot passage 23 to communicate with the reservoir17 via the channel 34 e, the annular window 34 d, and the through-hole34 h.

An opening provided in the outer tube 18 is installed with the sleeve 18a, and the solenoid Sol is housed in the bottomed cylindrical casing 35screwed to the outer circumference of the sleeve 18 a.

The solenoid Sol includes an annular solenoid bobbin 39 fixed to thebottom portion of the casing 35 with a coil 38 being wound around, abottomed cylindrical first fixed iron core 40 fitted to the innercircumference of the solenoid bobbin 39, a tubular second fixed ironcore 41 fitted to the inner circumference of the solenoid bobbin 39, anonmagnetic filler ring 42 interposed between the first and second fixediron cores 40 and 41 to form a gap between the first and second fixediron cores 40 and 41 and fitted to the inner circumference of thesolenoid bobbin 39, a tubular movable iron core 43 arranged in the innercircumferential side of the first fixed iron core 40, and a shaft 44fixed to the inner circumference of the movable iron core 43.

The casing 35 includes a tubular portion 35 a and a bottom portion 35 bfixed by caulking an opening end of the tubular portion 35 a. When theopening end of the tubular portion 35 a is caulked, a bobbin holder 36is fixed to the inner circumference of the tubular portion 35 a alongwith the bottom portion 35 b. The bobbin holder 36 holds the solenoidbobbin 39, and the solenoid bobbin 39 is installed in the casing 35using the bobbin holder 36.

As the casing 35 is screwed to the sleeve 18 a, the flange 41 a providedin the outer circumference of the second fixed iron core 41 isinterposed between the casing 35 and the sleeve 18 a. As a result, thefiller ring 42 and the first fixed iron core 40 are fixed inside thecasing 35.

The movable iron core 43 having a tubular shape has an innercircumference where the shaft 44 extending from both ends in the axialdirection is mounted. An annular guide 46 is fitted to the innercircumference of the second fixed iron core 41, and an annular bushing47 is held in the inner circumference of the guide 46. The shaft 44 isheld by annular bushings 45 and 47 provided in the bottom portion of thefirst fixed iron core 40 movably in the axial direction, so that thebushings 45 and 47 guides movement of the shaft 44 in the axialdirection.

As the second fixed iron core 41 is fixed to the casing 35 as describedabove, the guide 46 fitted to the inner circumference of the secondfixed iron core 41 abuts on the failsafe valve seat member 34. As aresult, the failsafe valve seat member 34, the pilot valve seat member21, the valve housing 20, and the valve seat member 1 are fixed to theshock absorber S. Since the failsafe valve seat member 34 has the notch34 g, the pilot passage 23 is not blocked even when the guide 46 abutson the failsafe valve seat member 34.

An end of the bushing 47 side of the shaft 44 abuts on the perforateddisc 32 fitted to the inner circumference of the annular projection 22 gof the pilot valve body 22. As a result, the biasing force of the coilspring 33 is also exerted to the shaft 44 via the pilot valve body 22.The coil spring 33 biases the shaft 44 serving as one of the elements ofthe solenoid Sol as well as the pilot valve body 22.

The second fixed iron core 41 has a tubular sleeve 41 b fitted to theinner circumference of the sleeve 18 a. As a result, each element of thesolenoid Sol is positioned in the radial direction with respect to thesleeve 18 a.

A notch (not shown) is provided in the outer circumference of thefailsafe valve seat member 34. As a result, a gap between the sleeve 41b and the failsafe valve seat member 34 is not blocked, so that it ispossible to sufficiently obtain an area of the flow path of the pilotpassage 23. In addition, the axial length of the sleeve 41 b is set soas not to interfere with the spool 30.

The guide 46 is provided with a hole 46 a penetrating in the axialdirection in order to prevent a pressure difference between the failsafevalve seat member 34 side and the movable iron core 43 side in the guide46. In addition, the movable iron core 43 is also provided with a hole43 a penetrating in the axial direction in order to prevent a pressuredifference between the guide 46 side and the bushing 45 side in themovable iron core 43 and hindrance of appropriate movement of themovable iron core 43.

The solenoid Sol is formed such that a magnetic path passes through thefirst fixed iron core 40, the movable iron core 43, and the second fixediron core 41, so that the movable iron core 43 arranged in the vicinityof the first fixed iron core 40 is attracted to the second fixed ironcore 41 side as the coil 38 is magnetically excited. That is, a thrustforce directed to the pilot valve Pi side is exerted to the movable ironcore 43.

The shaft 44 moving in synchronization with the movable iron core 43abuts on the pilot valve body 22 of the pilot valve Pi as illustrated inFIG. 1, so that the thrust force of the solenoid Sol is transmitted tothe pilot valve body 22. That is, when the solenoid Sol is magneticallyexcited, it is possible to exert a thrust force directed to the valveseat member 1 side from the movable iron core 43 to the pilot valve body22 via the shaft 44.

When the solenoid Sol is not magnetically excited, the pilot valve body22 is pressed by the coil spring 33, so that the pilot valve body 22 isunseated from the pilot valve seat 21 d to open the pilot valve Pi atmaximum. At the same time, the pilot valve body 22 is seated on theflange 34 f of the failsafe valve seat member 34 so as to block thepilot passage 23. As a result, the failsafe valve F functionseffectively.

The thrust force exerted to the pilot valve body 22 can be controlledbased on an electric current amount to the coil 38 of the solenoid Sol.As a result, it is possible to control the valve opening pressure of thepilot valve Pi.

A description will be made in more detail.

As an electric current is supplied to the solenoid Sol to exert a thrustforce to the pilot valve body 22, the pilot valve body 22 is pressed tothe pilot valve seat 21 d resisting to the biasing force of the coilspring 33.

As the upstream pressure of the pilot passage 23 is applied to the pilotvalve body 22, and a resultant force between the force of unseating thepilot valve body 22 from the pilot valve seat 21 d and the biasing forceof the coil spring 33 exceeds the thrust force of the solenoid Sol, thepilot valve Pi is opened so as to open the pilot passage 23.

That is, as the upstream pressure of the pilot passage 23 reaches thevalve opening pressure, the pilot valve Pi is opened so as to open thepilot passage 23. In this manner, by controlling the thrust force of thesolenoid Sol using the level of the electric current amount supplied tothe solenoid Sol, it is possible to control a level of the valve openingpressure of the pilot valve Pi.

As the pilot valve Pi is opened, the pressure of the pilot passage 23upstream from the pilot valve Pi becomes equal to the valve openingpressure of the pilot valve Pi. Accordingly, the pressure of theback-pressure chamber P obtained by introducing the pressure of thepilot passage 23 upstream from the pilot valve Pi is also controlled tothis valve opening pressure.

Subsequently, a description will be made for operation of the dampingvalve V.

As the shock absorber S expands or contracts so that the hydraulic oilis discharged from the rod-side chamber 13 to the reservoir 17 throughthe damping valve V, the pressures upstream of the port 1 a and thepilot passage 23 increase if the damping valve V is normally operated.Here, when the valve opening pressure of the pilot valve Pi iscontrolled by supplying an electric current to the solenoid Sol, thepressure of the pilot passage 23 between the orifice 1 f and the pilotvalve Pi is guided to the back-pressure chamber P.

The internal pressure of the back-pressure chamber P is controlled tothe valve opening pressure of the pilot valve Pi. Therefore, bycontrolling this valve opening pressure using the solenoid Sol, it ispossible to control the pressure applied to rear face of the valve body3. That is, it is possible to control the valve opening pressure forcausing the valve body 3 to open the port 1 a.

More specifically, as the internal pressure of the valve-bodyintermediate chamber C increases by the internal pressure of therod-side chamber 13, and the force of flexing the outer circumference ofthe valve body 3 surpasses the internal pressure of the back-pressurechamber P and the biasing force of the plate spring 27, the valve body 3is flexed and is unseated from the second valve seat 2 a. That is, a gapis formed between the valve body 3 and the subsidiary valve body 2 toopen the port 1 a.

As a result, it is possible to control the pressure of the valve-bodyintermediate chamber C for unseating the valve body 3 from the secondvalve seat 2 a by controlling the internal pressure of the back-pressurechamber P. That is, it is possible to control the valve opening pressureof the valve body 3 using the electric current amount supplied to thesolenoid Sol.

Therefore, as illustrated in FIG. 3, a damping characteristic of thedamping valve V (a characteristic of the damping force against thepiston speed) has a slight slope (as indicated by the plot X in FIG. 3)because the hydraulic oil passes through the sliding gap of the dampingvalve V and the orifice 3 a until the valve body 3 is opened. As thevalve body 3 is unseated from the second valve seat 2 a so as to openthe port 1 a, the slope is reduced as indicated by the plot Y. That is,a damping coefficient decreases.

Since the pressure boosting ratio of the valve body 3 is smaller thanthe pressure boosting ratio of the subsidiary valve body 2 as describedabove, the valve opening pressure of the valve body 3 is lower than thevalve opening pressure of the subsidiary valve body 2. Therefore, if thedifferential pressure generated by the restrictive passage 2 b does notreach the valve opening pressure for unseating the subsidiary valve body2 from the first valve seat 1 b, the subsidiary valve body 2 remains tobe seated on the first valve seat 1 b.

While the valve body 3 is flexed and opened, as the differentialpressure generated by the restrictive passage 2 b reaches the valveopening pressure for unseating the subsidiary valve body 2 from thefirst valve seat 1 b, by the piston speed of the shock absorber Sincreases, the subsidiary valve body 2 is also unseated from the firstvalve seat 1 b so as to open the port 1 a.

In this case, as the subsidiary valve body 2 is unseated from the firstvalve seat 1 b, the port 1 a directly communicates with the reservoir 17without using the restrictive passage 2 b. Therefore, an area of theflow path is enlarged, compared to the case where only the valve body 3is opened, and the port 1 a communicates with the reservoir 17 onlythrough the restrictive passage 2 b. Therefore, the slope of the dampingcharacteristic of the damping valve V is reduced as indicated by theplot Z in FIG. 3, compared to the case where only the valve body 3 isopened. That is, the damping coefficient further decreases.

If the valve opening pressure of the pilot valve Pi is changed bycontrolling the electric current amount to the solenoid Sol, the dampingcharacteristic of the damping valve V can be changed such that the plotsY and Z vertically move within a range indicated by the dotted lines inFIG. 3.

In the damping valve V, it is possible to set the pressure boostingratio of the valve body 3 to be lower than the pressure boosting ratioof the subsidiary valve body 2. As a result, the valve opening pressureof the valve body 3 becomes lower than the valve opening pressure of thesubsidiary valve body 2. That is, the damping valve V relieves the port1 a in two stages. Therefore, using the damping valve V, it is possibleto reduce the damping force for the full soft setting, in which thevalve opening pressure of the pilot valve Pi is set to the minimum, andwiden the damping force control range, compared to a damping valve ofthe prior art.

Using the damping valve V according to this embodiment, it is possibleto output a soft damping force and prevent an excessive damping forcewhen the piston speed of the shock absorber S is at a low speed range.In addition, it is possible to raise an upper limitation of the harddamping force desired when the piston speed is at a high speed range andprevent an insufficient damping force. Therefore, by applying thedamping valve V to the shock absorber S, it is possible to widen adamping force control range and improve a riding quality of a vehicle.

The internal pressure of the back-pressure chamber P is applied to theannular groove 20 c provided in the outer circumference of the valvehousing 20 to press the ring 29 mounted to the annular groove 20 c so asto enlarge its diameter. For this reason, a frictional force generatedbetween the spool 30 and the ring 29 making sliding contact with theinner circumference of the spool 30 increases as the electric currentsupply amount to the solenoid Sol increases, and the valve openingpressure of the pilot valve Pi increases.

That is, since a frictional force for suppressing the axial movement ofthe spool 30 with respect to the valve housing 20 increases, it isdifficult to open the subsidiary valve body 2 and the valve body 3.Therefore, as the valve opening pressure of the pilot valve Piincreases, a damping characteristic for the hard setting has a higherdamping coefficient than that of the damping characteristic for the softsetting.

If the ring 29 is provided in this manner, and the internal pressure ofthe back-pressure chamber P is applied to the inner circumference of thering 29, it is possible to widen the damping force control range for thehard setting and generate the damping force suitable for a dampingtarget in the shock absorber S. According to this embodiment, since thering 29 has the bias cut 29 a, it is possible to further suppressmovement of the spool 30. Therefore, it is possible to intensify aneffect of increasing the damping coefficient obtained by setting theback-pressure chamber P to a high pressure and increase a rise level ofthe damping coefficient.

Since the ring 29 is pressed toward the spool 30 by virtue of theinternal pressure of the back-pressure chamber P at all times, the ring29 also seals the gap between the spool 30 and the valve housing 20. Asa result, it is possible to control the internal pressure of theback-pressure chamber P as desired regardless of the clearance betweenthe spool 30 and the valve housing 20. Therefore, the damping forcegenerated by the damping valve V is stabilized without a variation.

In this manner, in the damping valve V according to this embodiment, thering 29 is provided to make sliding contact with the inner circumferenceof the spool 30, and the pressure of the back-pressure chamber P isapplied to the inner circumferential side of the ring 29. Therefore, itis possible to increase a damping force control range and exert a stabledamping force without a variation.

Although the port 1 a is opened in two stages by stacking the subsidiaryvalve body 2 on the valve seat member 1 and further stacking the valvebody 3 on the subsidiary valve body 2 according to this embodiment, thesubsidiary valve body 2 may be removed. If the subsidiary valve body 2is removed, a configuration may be employed such that the valve body 3is directly stacked on the first valve seat 1 b of the valve seat member1, the spool 30 abuts on the rear side of the valve body 3, and thevalve body 3 is biased toward the first valve seat 1 a using thepressure of the back-pressure chamber P. In this case, since only thevalve body 3 opens the port 1 a, the damping valve V makes the shockabsorber S have a damping characteristic illustrated in FIG. 4.

According to this embodiment, the pilot valve Pi has the pilot valveseat member 21 and the pilot valve body 22. The pilot valve seat member21 has the tubular valve container 21 a having the penetrating hole 21 cfor connecting the inside and the outside, and the annular pilot valveseat 21 d provided in the end of the valve container 21 a. The pilotvalve body 22 has the small diameter portion 22 a slidably inserted intothe valve container 21 a, the large diameter portion 22 b, and theconcave portion 22 c provided between the small diameter portion 22 aand the large diameter portion 22 b to face the penetrating hole 21 c.The pilot valve Pi is configured such that the end of the large diameterportion 22 b of the pilot valve body 22 is seated on or unseated fromthe pilot valve seat 21 d of the pilot valve seat member 21.

As a result, using the pilot valve Pi, it is possible to reduce an areaA of the pressure applied to extract the pilot valve body 22 from thepilot valve seat member 21 as illustrated in FIG. 5 and enlarge an areaof the flow path during the valve opening operation.

Here, a description will be made for a distance between the valve bodyof the pilot valve and the valve seat when the pilot valve Pi isconfigured similar to the damping valve of the prior art discussed inthe JP 2009-222136 A, in which only the port is opened or closed by apoppet valve.

Since an inertial force is also applied to the valve body, a position ofthe valve body in this case is once set to a dynamically overshotposition rather than the statically balanced position, in which thethrust force of the solenoid, the biasing force of the coil spring forbiasing the valve body, and the force of pressing the valve body byvirtue of the upstream pressure of the pilot valve are staticallybalanced. Then, the position of the valve body is displaced in avibration sense over the statically balanced position and is convergedto a balanced position.

That is, in the pilot valve of the damping valve of the prior art, sincean area of the flow path is smaller relative to the valve opening levelof the pilot valve, the clearance between the pilot valve and the valveseat easily increases, and a long time is necessary until the valve bodyis stabilized in the statically balanced position (indicated by theone-dotted chain line in FIG. 6) after the pilot valve is opened asindicated by the dotted line in FIG. 6. In addition, since the overshootis significant as described above, the generated damping force changessteeply, and it takes time until the damping force is stabilized.

Such a problem may be addressed by increasing the area of the flow pathrelative to the valve opening level of the pilot valve. However, in thedamping valve of the prior art, since the pilot valve is the poppetvalve, it is necessary to enlarge a diameter of the annular valve seatwhere the poppet valve is seated or unseated in order to increase thearea of the flow path. In this case, since an area of the pressureapplied to unseat the poppet valve from the valve seat increases, it isnecessary that the solenoid output a strong thrust force. This increasesthe size of the damping valve disadvantageously.

In comparison, in the pilot valve Pi according to this embodiment, it ispossible to enlarge the area of the flow path relative to the clearancebetween the pilot valve body 22 and the pilot valve seat 21 d while thearea of the pressure for separating the pilot valve body 22 from thepilot valve seat 21 d is reduced. Therefore, it is possible to reducethe time taken to stabilize the pilot valve body 22 to the staticallybalanced position without increasing the size of the solenoid Sol asindicated by the solid line in FIG. 6. Accordingly, the size of thedamping valve V does not increase as well. Furthermore, it is possibleto suppress an abrupt change of the damping force of the damping valve Vand exert a stable damping force with excellent responsiveness.

In the damping valve V, the internal pressure of the back-pressurechamber P is controlled by exerting the thrust force to the pilot valvePi depending on the electric current supplied to the solenoid Sol, so asto control the valve opening pressures of the subsidiary valve body 2and the valve body 3. Therefore, it is possible to control the internalpressure of the back-pressure chamber P without depending on the flowrate of the hydraulic oil flowing through the pilot passage 23. As aresult, a change of the damping force against the electric currentsupplied to the solenoid Sol becomes linear even when the piston speedof the shock absorber S stays at a low speed range. Therefore, it ispossible to improve controllability. Furthermore, since the internalpressure of the back-pressure chamber P for biasing the valve body 3 iscontrolled by exerting the thrust force to the pilot valve Pi dependingon the electric current supplied to the solenoid Sol, it is possible toreduce a variation of the damping force.

In the damping valve V, in the event of a failure, the electric currentsupplied to the solenoid Sol is shut down, and the pilot valve body 22is pressed by the coil spring 33, so that the opening end of thefailsafe valve seat member 34 opposite to the valve housing 20 isclosed.

In this case, as the internal pressure of the rod-side chamber 13reaches the valve opening pressure, the failsafe valve F is opened, andthe pilot passage 23 communicates with the reservoir 17, so that thefailsafe valve F applies resistance to the flow of the hydraulic oil.Therefore, the shock absorber S can serve as a passive shock absorber.It is possible to set the damping characteristic of the shock absorber Sas desired in advance by setting the valve opening pressure of thefailsafe valve F.

According to this embodiment, the valve opening pressures of thesubsidiary valve body 2 and the valve body 3 are controlled bycontrolling the pressure of the back-pressure chamber P using thesolenoid Sol. However, it is possible to reduce the pressure boostingratio of the valve body 3 to be lower than the pressure boosting ratioof the subsidiary valve body 2 without controlling the valve openingpressure of the pilot valve Pi using the solenoid Sol even when thepilot valve Pi is a passive pressure control valve, that is, even whenthe pressure of the back-pressure chamber P is not controlled.

Therefore, since the damping characteristic of the shock absorber S canchange in two stages, it is possible to output a soft damping force andprevent an excessive damping force when the piston speed is at a slowspeed range. In addition, it is possible to output a hard damping forceand prevent an insufficient damping force when the piston speed is at ahigh speed range.

In addition, since the subsidiary valve body 2 is floatably stacked onthe valve seat member 1, it is possible to open the port 1 a across awide area and reduce the damping coefficient when the subsidiary valvebody 2 is opened. Therefore, it is possible to easily control thedamping force using the solenoid Sol.

Furthermore, since the valve body 3 is an annular leaf valve having aninner circumference fixed to the valve seat member 1 and an outercircumference seated on or unseated from the second valve seat 2 a, thismakes it easy to bias the subsidiary valve body 2 to return thesubsidiary valve body 2 to the sitting position of the first valve seat1 b after the port 1 a is opened. As a result, it is possible to preventa delay in closing the port 1 a when the shock absorber S expands orcontracts frequently.

Therefore, it is possible to improve responsiveness for generating adamping force and remove necessity of installing a spring forfacilitating returning of the subsidiary valve body 2. The valve body 3may be floatably mounted to the valve seat member 1 in a disc-like shapeas in the subsidiary valve body 2 of this embodiment instead of the leafvalve.

Since the first valve seat 1 b has an annular shape, and the innerdiameter of the second valve seat 2 a is larger than that of the firstvalve seat 1 b, it is possible to obtain a state in which the valve body3 is opened, and the subsidiary valve body 2 is not opened. Therefore,it is possible to obtain a damping characteristic of the damping valve Vrelieved in two stages. In addition, since both the first and secondvalve seats 1 b and 2 a have an annular shape, it is possible to easilydesign the pressure boosting ratio of the subsidiary valve body 2.Although it is possible to easily design the pressure boosting ratio byproviding the first and second valve seats 1 b and 2 a having an annularshape, they may have any shape other than the annular shape.

The damping valve V has the back-pressure chamber P provided in the sideof the valve body 3 opposite to the main valve seat and biases the valvebody 3 using the internal pressure of the back-pressure chamber P.Therefore, it is possible to prevent a variation of the valve openingpressure of the valve body 3 between each product by managing adimension of the member for forming the back-pressure chamber P, exert astable biasing force to the valve body 3, and exert a strong biasingforce to the valve body 3.

Since the damping valve V has the pilot passage 23 for reducing thepressure upstream of the port 1 a and guiding it to the back-pressurechamber P, it is possible to set the valve opening pressures of thesubsidiary valve body 2 and the valve body 3 using the pressure upstreamof the port 1 a. In addition, since the damping valve V has the pilotvalve Pi for controlling the internal pressure of the back-pressurechamber P, it is possible to obtain a variable damping force bycontrolling the valve opening pressures of the subsidiary valve body 2and the valve body 3.

Although the pressure of the port 1 a is reduced and is guided to theback-pressure chamber P using the orifice 1 f provided in the pilotpassage 23 in this embodiment, any type of valve such as a choke valveother than the orifice may be used to reduce the pressure.

Next, a description will be made for a damping valve V2 according toanother embodiment of this invention.

In the damping valve V, the subsidiary valve body 2 having an annularshape is slidably mounted to the outer circumference of the spacer 25and is floatably installed to the valve seat member 1 as describedabove. In comparison, the damping valve V2 may be provided with asubsidiary valve body biasing means 50 for biasing the subsidiary valvebody 2 toward the valve seat member 1 as illustrated in FIG. 7.

Specifically, the subsidiary valve body biasing means 50 is a discspring interposed between the spacer 25 and the valve body 3 to bias thesubsidiary valve body 2 to be seated on the first valve seat 1 bprovided in the valve seat member 1. Other elements of the damping valveV2 are similar to those of the damping valve V. Therefore, theirdescriptions will not be repeated while like reference numerals denotelike elements.

In the damping valve V2, since the subsidiary valve body 2 is biased bythe subsidiary valve body biasing means 50, it is possible to make iteasy to return the subsidiary valve body 2 to the sitting position onthe first valve seat 1 b after the subsidiary valve body 2 opens theport 1 a. In addition, since the subsidiary valve body biasing means 50makes it easy to return the subsidiary valve body 2 even when the valvebody 3 and the subsidiary valve body 2 are separated from each other, itis possible to prevent a delay in closing the port 1 a when the shockabsorber S expands or contracts frequently. Therefore, it is possible tofurther improve responsiveness for generating the damping force.

It is noted that the subsidiary valve body biasing means 50 may beformed of any elastic body such as a spring or rubber other than thedisc spring if it can be configured such that the biasing force isexerted to return the subsidiary valve body 2 to the sitting position onthe first valve seat 1 b.

In the damping valve V3 according to still another embodiment, thesubsidiary valve body biasing means may be integrated into a subsidiaryvalve body 51 as illustrated in FIG. 8.

The subsidiary valve body 51 includes an annular outer ring portion 52seated on or unseated from the first valve seat 1 b and provided with asecond valve seat 52 a, and an annular inner ring portion 53 serving asthe subsidiary valve body biasing means. Other elements of the dampingvalve V3 are similar to those of the damping valve V. Therefore, theirdescriptions will not be repeated while like reference numerals denotelike elements.

The subsidiary valve body 51 is mounted to the outer circumference ofthe assembly shaft 1 c of the valve seat member 1 via an inner ringportion 53 formed of a thin plate into the inner circumferential side.The inner ring portion 53 is configured such that its outercircumferential side can be freely flexed if its inner circumferentialside is fixedly supported by the assembly shaft 1 c. For this reason, inthe damping valve V3, washers 54 and 55 are mounted to the assemblyshaft 1 c instead of the spacer 25 in order to hold the innercircumference of the inner ring portion 53 using the washers 54 and 55.In addition, the inner ring portion 53 is provided with a restrictivepassage 53 a serving as an orifice so as to cause the valve-bodyintermediate chamber C to communicate with the port 1 a.

The outer ring portion 52 having an annular shape includes an annularsecond valve seat 52 a provided in its outer circumference to protrudeoppositely to the valve seat member 1, and an annular concave portion 52b, where the outer circumference of the inner ring portion 53 is fitted,provided in its inner circumference opposite to the valve seat member 1.The subsidiary valve body 51 is configured such that the outer ringportion 52 is positioned by the inner ring portion 53 in the radialdirection so as not to be deviated.

In this manner, even when the inner ring portion 53 serving as asubsidiary valve body biasing means is integrated into the subsidiaryvalve body 51 itself, the subsidiary valve body 51 itself is biased bythe inner ring portion 53, so that it is possible to make it easy toreturn the outer ring portion 52 to the sitting position on the firstvalve seat 1 b after the outer ring portion 52 opens the port 1 a. Inaddition, even when the valve body 3 is separated from the outer ringportion 52, the inner ring portion 53 makes it easy to return the outerring portion 52. Therefore, it is possible to reliably prevent a delayin closing the port 1 a when the shock absorber S expands or contractsfrequently. In addition, it is possible to further improveresponsiveness for generating a damping force.

Embodiments of the present invention were described above, but the aboveembodiments are merely examples of applications of the presentinvention, and the technical scope of the present invention is notlimited to the specific constitutions of the above embodiments.

With respect to the above description, the contents of application No.2013-050136, with a filing date of Mar. 13, 2013 in Japan, areincorporated herein by reference.

The invention claimed is:
 1. A damping valve comprising: a valve seatmember provided with a port; a valve body that opens or closes the port;a tubular spool that abuts on a side of the valve body opposite to thevalve seat member; a spool holding member that has an outercircumference where the spool is mounted movably along an axialdirection; a ring mounted to the outer circumference of the spoolholding member, the ring contacting slidably with an inner circumferenceof the spool; and a back-pressure chamber partitioned by the spool andthe spool holding member, the back-pressure chamber being configured tobias the spool such that the valve body is pressed toward the valve seatmember using an internal pressure, wherein the internal pressure of theback-pressure chamber is applied to an inner circumferential side of thering.
 2. The damping valve according to claim 1, wherein the ring has abias cut.
 3. The damping valve according to claim 1, further comprisinga pilot passage configured to reduce a pressure upstream of the port andguide the pressure into the back-pressure chamber.
 4. The damping valveaccording to claim 3, further comprising a pilot valve configured tocontrol the internal pressure of the back-pressure chamber.
 5. Thedamping valve according to claim 1, wherein the valve seat member has afirst valve seat that surrounds the port, the damping valve furthercomprising a subsidiary valve body seated on or unseated from the firstvalve seat, the subsidiary valve body having a second valve seat in aside opposite to the valve seat member, the valve body is seated on orunseated from the second valve seat and forms a valve-body intermediatechamber between the subsidiary valve body and the valve body in an innercircumferential side of the second valve seat, the damping valve furthercomprising a restrictive passage that causes the port and the valve-bodyintermediate chamber to communicate with each other, the restrictivepassage being configured to apply resistance to a passing fluid flow,and the spool presses the subsidiary valve body toward the valve seatmember along with the valve body.
 6. The damping valve according toclaim 5, wherein the subsidiary valve body is floatably stacked on thevalve seat member.
 7. The damping valve according to claim 5, furthercomprising a subsidiary valve body biasing means configured to bias thesubsidiary valve body toward the valve seat member.
 8. The damping valveaccording to claim 5, wherein both the first and second valve seats havean annular shape, and an inner diameter of the second valve seat is setto be larger than that of the first valve seat.
 9. The damping valveaccording to claim 5, wherein the restrictive passage is formed in thesubsidiary valve body.
 10. The damping valve according to claim 1,wherein the valve body is an annular leaf valve having an innercircumference fixed to the valve seat member and an outer circumferencethat can be flexed.